Prior to being incorporated into consumer products, electronic devices, such as integrated circuit chips, are subjected to a variety of electrical tests designed to determine whether they operate properly. Sophisticated methods to assess the integrity of electronic devices use automation to quickly perform the desired analyses. For integrated circuits, the tests may be executed on the devices while still part of a semiconductor wafer on which the device is manufactured or on the device after is packaged. Testing may influence the manufacturing steps performed on a specific device, with some devices being discarded or, where devices are manufactured with redundant circuitry that can be used to replace faulty circuitry, routed to a rework station for repair. In some manufacturing operations, based on the results of testing, a device may be “binned”, with devices that operate, but below specifications, being binned for labeling and sale as reduced functionality parts.
Tests often comprise a wide variety of analyses, whether in the analog or digital domain. For example, the following analyses may be performed: open/short circuit test, bit error rate test, address line test, data line test, random number sequence, random moving inversion, and jitter analysis. Combinations of these analyses may determine whether the overall device under test (DUT) operates properly, and, if not, may identify the defective portions of the DUT. In addition to being useful for binning parts, the information obtained through the analyses may be used to improve manufacturing yields.
To meet the throughput needed for economic manufacture of semiconductor devices, tests are typically performed on a large number of units in parallel. A piece of automatic test equipment, referred to as a “tester,” may be used to generate test signals that stimulate multiple DUTs and to measure the responses. The tester may determine whether each DUT is operating properly by comparing the response evoked to a carefully controlled test pattern with an expected response.
To test DUTs completely, the tester should generate and measure signals such as may be found in the operating environment of those DUTs. Test equipment is typically made with multiple instruments. Each instrument may perform a specific function, such as generating high speed digital signals or producing an analog waveform that has a programmed characteristic. Multiple instruments are installed in a tester to provide the combination of analog and digital signals needed to test a particular device. Creating instruments that provide separate test functions provides a flexible way to configure a test system to generate and measure a set of test signals required for testing any of a wide variety of semiconductor devices.
Though the functions of a test system may be configured by the selection of instruments installed in the test system, the inputs and outputs points of these instruments are arrayed in a known pattern, which is unlikely to match the connections on devices to be tested. A tester interface unit (TIU) may be used to connect the input and output points on the tester to one or more devices under test. The TIU may be constructed with a tester interface and a device interface, with signal-carrying conductors running between them. The tester interface may provide connections that are aligned with the inputs and the outputs of the tester. The device interface may have sockets, probe needles or other structures to make contact to the devices under test. The signal carrying conductors may be cables or other flexible conductors, enabling a “space transformation” between the device interface and the tester interface, such that the configuration of contact points at the device under test can be independent of the configuration of contact points at the test system. The cables also provide for high signal integrity, which is necessary to test high performance devices.
In some instances, an interface between a test system and a device under test may be implemented with a device interface board (DIB). A DIB may be one or a stack of printed circuit boards, which is likely to provide lower signal integrity than a TIU. In some instances, custom test circuitry may be mounted on the printed circuit board used as a DIB. This approach may be used, for example, when a function needed to fully test a DUT is not sufficiently common to design an instrument in a test system that performs this function. Accordingly, the custom circuitry on the DIB is self-contained, with any hardware necessary for generating and measuring test signals and controlling that hardware to perform the test function.